Motor vehicle emissions are a leading source of air pollution in many metropolitan areas. As a result, considerable effort and resources are currently devoted to various emission reduction strategies, such as emission inspection programs, reformulated or alternative fuels, stricter standards for new vehicles, mass transit, improved engine control and catalyst technologies, upgrade and repair of existing vehicles, and emission reduction credits aimed at providing a financial incentive to reduce emissions. However, in order to evaluate the impact of these reduction strategies and take advantage of emissions credits, it is necessary to measure and collect accurate real-world emission measurements over the life of a vehicle.
It is known that emission testing may be performed in a specialized laboratory, where the vehicle is driven on a dynamometer according to a prescribed driving cycle, such as I/M 240 or FTP for light and medium duty vehicles and CBD for heavy duty vehicles. This approach has several significant disadvantages, including that the driving cycles do not adequately represent real-world driving conditions, which vary and are often unknown.
Mobile testing systems that are attached to the vehicle are also known. For example, an on-board testing system mounted on a dedicated instrumented vehicle was disclosed by Sierra Research. This system used a repair-grade four-gas non-dispersive infra-red (NDIR) analyzer to measure exhaust gas concentrations and several sensors mounted on the engine to determine intake air flow. From these measurements, exhaust mass flow and mass emissions can be computed.
A simpler system, using repair grade NDIR analyzer concentration data only, was developed at the University of Denver to predict I/M 240 mass emissions. Using this system, the average ratio of pollutant to fuel consumed can be calculated from the concentration data. The amount of fuel consumed can then be estimated from the length of the trip and fuel economy. While this method was successful in predicting whether a vehicle would pass or fail an I/M 240 test, and has been incorporated into newer repair grade analyzers, it was not sufficiently accurate in measuring actual mass emissions, since it did not properly account for emissions during extreme (high or low) exhaust flow.
In recent years a number of portable emissions measurement systems (PEMS) have been developed. A PEMS is an onboard testing system or device that measures the emissions from mobile source while the source is an actual, real-world use, rather that in a laboratory or simulated environment.
The AXION™ device manufactured by GlobalMRV, Inc., of 3000 Sound Avenue, Riverhead, N.Y. 11901, is a commercially available PEMS. This system is capable of measuring mass emissions on a variety of vehicle engines during actual, real world and regular use and operation. The unit provides HC, CO, CO2, NOx and O2 readings for gasoline powered vehicles and NOx, CO, CO2, O2 and PM (light scattering) readings for diesel vehicles. The pollutant concentrations are obtained from a sample probe inserted into the tail pipe. This data is then combined with exhaust flow data calculated using engine parameters read from the vehicles engine control unit to determine mass emissions.
U.S. Pat. No. 6,308,130, entitled “Portable On-Board Mass Emissions Measuring System,” discloses a PEMS for measuring mass emissions. U.S. Pat. No. 6,435,019, entitled “Portable On-Board System for Measuring Vehicle Exhaust Particulate Emissions,” discloses a PEMS that measures emissions of particulate matter. The disclosure of each of U.S. Pat. No. 6,308,130 and U.S. Pat. No. 6,435,019 are incorporated in their entirety herein by reference.
The SPOT unit provided by Analytical Engineering, Inc., of 2555 Technology Boulevard, Columbus, Ind. 47201, is another commercially available PEMS. The SEMTECH® unit provided by Sensors, Inc., of 6812 S. State Road, Saline, Mich. 48176, is yet another alternative. For particulate matter, the SCANNING MOBILITY PARTICLE SIZER™ manufactured by TSI, Inc., of 500 Cardigan Road, Shoreview, Minn. 55126, is another commercially available PEMS system. A FTIR gas analyzer is also commercially available, such as the TITAN FTIR gas analysis system manufactured by MIDAC Corporation, of 130 McCormick Avenue, Costa Mesa, Calif. 92626.